FMS 13, running WebDirect fairly happily for about 30 clients on and off, but with occasional unexplained disconnects.

Thought we'd take a look in the WPE log to see if there was anything there that might shed some light - and there wasn't. In fact, there wasn't anything there at all. Yes, there's a log file, but it's empty with no contents. Tried shutting down the server, deleting the log file, and restarting the server, and the file is recreated, but still no entries.

Are we wrong to assume that the WPE conttains info regarding issues wiht WebDirect?

You have to enable access logging. Even access logging though won't necessarily log disconnect errors. If you think about it, a user getting disconnected via their side of the connection just looks like any other force disconnect from filemaker server for webdirect (such as closing a browser tab or exiting a browser), so it's not really recording any special events.